Workers are familiar with the use of servo tracks, recorded on moving disks. Servo information is recovered from such tracks by a transducer, and then may be decoded to indicate any positional deviation of the transducer from a center-track position. Such techniques are well known for finding specific locations, or benchmarks, along disk tracks and thereby reduce head-positional errors in the placing of a head over the disk, or bring the head into some registration. Such methods are also used to position read/write transducers over other moving media. U.S. Pat. No. 3,691,543 to Mueller shows such a system, as does U.S. Pat. No. 4,380,033 to Bacamia.
Workers recognize that various kinds of servo tracks have been used, depending on the application; ranging from "dedicated" tracks, containing nothing but position information, to signal storage tracks, with servo information interspersed among stored data signals, to data storage tracks which themselves provide servo information where special means are provided to interpret the servo-signals.
Various forms of servo readback signals are also known. One is the sophisticated, two element so-called "tribit" track (e.g., taught by Mueller in U.S. Pat. No. 3,691,543.
The Mueller system postulates a disk with a servo track, a transducer for picking up two position-indication signals from the servo track, a servo for positioning the transducer, and a feedback circuit with a two-channel demodulator for separating the two position indicating signals, comparing them, and responsively generating a feedback signal to the servo. As the transducer approaches and crosses the servo track, the position-indicating signals change, altering the comparator signal to in turn, modify the servo signal.
For these and other reasons, it is usually desirable to provide means for enhancing the precision of the servo signals. This teaching is so oriented.
Here taught is a servo signal format especially apt for use with thin film magnetic R/W transducers and with a "Quad" type positioning code. Among other advantages, this will be seen to enhance linearity of servo response and to help reduce error due to servo-track offset (e.g., eliminating tail-overshoot, using "timing" signals to isolate position signals).